Is UDP routable?

Legacy User

Is UDP routable? I came across this question in an exam demo. I said no, and was marked wrong. Clearly an error, thinks I.

Then I remembered seeing another question which said that in IPX/SPX the equivalent of UDP is IPX.

If that is correct then maybe UDP is routable...

Any thoughts, anyone?

Pavlov

UDP (User Datagram Protocol) is a communications protocol that offers a limited amount of service when messages are exchanged between computers in a network that uses the Internet Protocol (IP). UDP is an alternative to the Transmission Control Protocol (TCP) and, together with IP, is sometimes referred to as UDP/IP. Like the Transmission Control Protocol, UDP uses the Internet Protocol to actually get a data unit (called a datagram) from one computer to another. Unlike TCP, however, UDP does not provide the service of dividing a message into packets (datagrams) and reassembling it at the other end. Specifically, UDP doesn't provide sequencing of the packets that the data arrives in. This means that the application program that uses UDP must be able to make sure that the entire message has arrived and is in the right order. Network applications that want to save processing time because they have very small data units to exchange (and therefore very little message reassembling to do) may prefer UDP to TCP. The Trivial File Transfer Protocol (TFTP) uses UDP instead of TCP.
UDP provides two services not provided by the IP layer. It provides port numbers to help distinguish different user requests and, optionally, a checksum capability to verify that the data arrived intact.

In the Open Systems Interconnection (OSI) communication model, UDP, like TCP, is in layer 4, the Transport Layer.


With that said, do you think it's routable? Not trying to be a smartass, just trying to give a specific definition for the protocol and force you to think about it.

eucharist

Okay, here's what I've come up with. Movin' down the OSI stack, we have TCP segments being tucked into IP datagrams which are then stuffed into little paper hats, I mean data frames, and send on their way across the network.

So whether it's TCP or UDP, it doesn't matter, they both start out from the Transport layer and they're both double-wrapped by the time they set out. When they're unpackaged at the other end, TCP goes directly to a port but ol' UDP, he just starts hollering.

So, does that mean UDP is routable? Not any more than TCP is routable. In other words, the question is meaningless, since neither actually participate in routing.

Am I right?

Hey, wait a minute, I just remembered there are UDP ports as well as TCP ports. So why is UDP shouting then?

I can't figure this stuff out. I think there's a bottleneck in my brain.

Help!

the Bard

UDP is Routable...

unless I am badly mistaken, think of it to TCP as TFTP(Trivial File Transfer protocol) is to FTP

UDP and TFTP (I cant think of the proper term)

both do not verify packets and transmission whereas TCP andFTP do

the Bard

oops... pavlov, next time I'll read your post instead of skimming over it... and then saying what you just said

Webmaster

So, does that mean UDP is routable? Not any more than TCP is routable. In other words, the question is meaningless, since neither actually participate in routing.

Am I right?

Yes. TCP and UDP are Transport layer protocols. TCP and UDP datagrams are encapsulated in IP packets (which are.... routable) when they travel down the OSI model(at Layer 3 Network)

eucharist

Actually, Pavlov, your admonition to work it out myself has set gears in motion. You know how it is when you first learn this stuff. They pour it into your head and you understand the individual bits, but it's hard to put it all together.

For example, we know that the TCP/IP and the Internet use packet-switching. This means that routing occurs at the Network layer. Thus, all along I've had this picture in my head of packets whizzing about from router to router.

But it now seems that I must be mistaken. After all, it is frames that get sent out over the wire, is it not? And frames, my text book tells me, have a source and destination address. The book doesn't elaborate on exactly what kind of address but I must assume that it is not an IP address (that's only found at the network layer) so it must be a MAC address.

Whatever it is, it's enough to get the frame to the next node. So really what we have is a frame-switched network, right? UNLESS, at each node, the frame is unwrapped to reveal the IP address, which is then used to plot the route to the next node...

But why bother, if the address in the frame is enough to get it to the next node?

Can anyone shed any light on this?

Legacy User

hey eucharist

Yes when working on the local level a frame is sent that includes an address - BUT you have to remember that is a MAC address and is stripped from the frame before going out on the network (assuming here we are on the same wavelength and not just talking a small LAN).
UDP packets are smaller and simpler than TCP and transmit far less information. Also remember that they are connectionless and therefore do not guaruntee delivery.
But I digress - as a part of the TCP/IP protocal UDP is routeable.

eucharist

cool!

except, like, i thought it was settled (in an earlier post) that udp is NOT routable, any more than TCP is routable, because routing occurs at the Network layer, and UDP and TCP are a couple of happening dudes at the Transport layer.

i realize that in the real world things do not conform to the OSI model in a neat and tidy fashion. i can accept that.

it's just that i've a network+ exam to write very soon, and i'm wonderin' where our brothers at ClompTIA might weigh in on this...

cheers

RussS

Sorry dood - I was guest - guess I forgot to log in.
The following is from my study notes. I passed Net+ last week.

UDP
· Created by the people who made TCP/IP
· UDP (User Datagram Protocol)
· Simpler and smaller than TCP/IP
· Connectionless
. Routeable

Webmaster

I was just going over this post again, and I noticed I didn't confirm this at all, but I will... with certainty:

UDP is routable.

UDP is a routable transport protocol, TCP and SPX are as well, NETBEUI is non-routable. (I was actually writing the latter part down for a Network+ TechNote about protocols when I remembered this post, something similar to this:
...NETBIOS (Session layer API) and NETBEUI (NETBios Extended User Interface, a non-routeable Transport layer protocol), used to be considered as one set of protocols, Microsoft and Novell separated the two so NETBIOS could be used in combination with other Transport protocols that are routable such as UDP and TCP...

It does need IP to be routed...

Johan